This application relates to a print hammer for high speed printers, and more particularly, for high speed printers wherein the type-face-carrier is moved in front of the print hammer for character selection purposes.
The general requirement for high speed printers is to print as many characters in a second as possible and this means a high cyclic rate. In impact printers using movable type-face-carriers, printing is achieved by moving the type-face-carrier to present the character to be printed in front of a print position and then driving a print hammer from a rest position to an impact position wherein a character printing element borne by said type-face-carrier is struck onto a recording medium held by a platen cylinder. Prior to any start of subsequent printing, the print cycle has to be completed, i.e., the hammer has to go back to its rest position before the type-face-carrier can be moved to present the next character to be printed, in front of the next print position.
For instance, printers are known in which the type-face-carrier is made of a printwheel provided with radially extending resilient pads or fingers each of which bears a character printing element on its extremity. Proper positioning of a pad for printing purposes involves two movements, a rectilinear shifting movement of the print-wheel along the platen and a rotary movement of the printwheel to present the desired pad in front of the print hammer. The printing speed may be increased by having these two movements overlapping each other in time, i.e., the printwheel is rotated while being shifted. However, since printing is performed by having the print hammer strike a pad against the printing medium, any printwheel rotation is prohibited until the printwheel path has been cleared by the return of the print hammer. One way of reducing the time the print hammer interferes with the path of the rotatable printwheel is by positioning the printwheel as close to the platen as possible, but this reduces the printline visibility, which, from a user's standpoint is a great disadvantage.
Another way for reducing the time the print hammer prohibits the printwheel from being rotated while said print hammer is in print position, is by articulating the hammer head. Such a hammer has been disclosed in the U.S. Pat. No. 3,651,916 assigned to Ing. C. Olivetti by Raffaele Becchi. Becchi's hammer is provided with head articulated for being movable in a horizontal plane. With such an implementation, the printwheel can be positioned a little further away from the platen since rotation of said printwheel is not completely prohibited by the hammer returning to its rest position. This supposes, however, that the printwheel is to be rotated in one direction only. In addition, the printwheel cannot be positioned too far away from the platen otherwise interference between the hammer head returning to its rest position and the printwheel path might be too long in time, which means that several fingers might hit the hammer head while the printwheel is being rotated, which could result in printwheel damaging, unless the printing speed is being reduced.